Older Men’s Sperm May Have Disease-Causing Mutations

There is a new warning for men who are thinking of delaying fatherhood.

Scientists at University of Oxford in the UK have identified a source of some severe disease-causing mutations in sperm-producing tubes inside the testicles of healthy men.

Sperm production starts in puberty, in the seminiferous tubules inside the testicles. A man's testicles produce millions of sperm and new spermatogonia every day.

At each cell cycle, the DNA in the old spermatogonium is copied into the new cells -- destined to be a sperm cell. But every so often, a copy error -- a mutation -- arises in the DNA, which carries on in new generations of cells.

Many mutations are harmless, but some that occur in the spermatogonia enhance their own chances of propagating forward -- they are called "selfish mutations." It appears that the effect of selfish mutations is to cause spermatogonia to give rise to more than one new spermatogonium at each cell cycle, each carrying the mutation.

As a man ages, and his sperm production undergoes more cell cycles, his sperm contains an increasing proportion of cells with selfish mutations.

The study investigated a rare genetic disease called Apert syndrome that affects the development of the skull and limbs. The disease affects about 1 in 60,000-70,000 babies. It’s caused by new mutations in a gene called FGFR2 that arise spontaneously in the father's sperm production as he gets older.

The researchers note that all men will develop these mutant growths in their testicles as they age. However, as men are tending to delay fatherhood, it is important to understand the risks.